This application claims priority from French Patent Application Serial No. 98-10557 filed on Aug. 19, 1998, which is incorporated herein by reference.
1. Field of the Invention
The subject of the present invention is a deformable transverse member for a motor vehicle rear axle assembly, especially a rear axle assembly with trailing arms.
2. Description of Related Art
Of all the technical solutions regarding motor vehicle rear axle assemblies, the semirigid axle is a simple and economical solution because, in one component, it provides the wheels of the rear axle assembly with guidance and fulfils the anti-roll function.
In general, the semi-rigid axle is made up of two trailing arms connected by a transverse member.
The assembly thus formed is attached to the body of the vehicle via two elastic mounts.
The transverse member is connected rigidly to the arm usually by two gusset plates each fixed, on the one hand, to the end of the transverse member and, on the other hand, to the corresponding trailing arm, generally by welding.
The distance from the ends of the arm at which the transverse member is positioned varies according to the configuration of the vehicle rear axle assembly. This position depends on the overall architecture of the vehicle substructure and, in particular, depends on the location of the fuel tank. To fulfill its dual role of providing guidance and acting as an antiroll bar, this transverse member must have a given rigidity particularly in torsion and in bending so as to obtain an ideal compromise between the road holding ability of the vehicle and the comfort of the passengers, particularly in the case of a touring vehicle.
Specifically, the use of an excessively rigid transverse member prevents practically all vehicle body roll, but causes jolts which are uncomfortable for the passengers, and sometimes is associated with a wheel lifting off the ground, which is detrimental to the road holding of this vehicle.
The use of an excessively flexible transverse member prevents any lifting of the wheels during normal driving of the vehicle, but generates a phenomenon of significant roll which is also dangerous for the passengers.
Most deformable transverse members for trailing arm rear axle assemblies have a cross section which, along their entire length, exhibit a profile of the so-called open section type, for example in the overall shape of a C, a U or a V.
This type of transverse member has the particular feature of offering torsional rigidity that is compatible with the sought-after values limiting vehicle body roll while at the same time providing good road holding ability.
In an effort to reduce the weight of the vehicle, manufacturers have been decreasing the wall thickness of the transverse member within the possible limits dictated by the mechanical strength of this transverse member, but this reduction in wall thickness on an open-section transverse member does, nonetheless, lead to a significant reduction in the torsional stiffness of this transverse member, thus increasing the possibilty of vehicle body roll.
So, to maintain the same vehicle characteristics, particularly as regards roll, manufacturers wishing to restrict the weight of the vehicles have been forced to complement the open-section transverse member with a device for limiting roll, for example an antiroll bar.
Another solution could consist in using a transverse member with a closed cross section along its entire length, but with reduced wall thickness.
However, to exhibit a torsional stiffness that is compatible with the sought-after values in order to obtain a compromise between the road holding ability of the vehicle and desired the level of passenger comfort, it would be necessary either to reduce greatly the cross section of the transverse member or to keep the same cross section while reducing the wall thickness or to reduce both the cross section and the wall thickness of the transverse member.
Such a reduction in thickness is incompatible with the mechanical strength of the transverse member, even if a steel with a high elastic limit is used.
Likewise, reducing the cross section of the transverse member would generate very high stresses at the connection between this transverse member and the arm of the axle.
For this reason, French Patent No. 2,745,240 discloses a transverse member for a rear axle assembly which comprises a central region in which the cross section of this transverse member is a closed profile and two lateral zones in which the cross section of this transverse member is an open profile.
However, this type of transverse member has drawbacks, the main drawback lying in the fact that the stresses generated at the interfaces between the open zones and the closed central zone are high as will be seen later. These stresses may cause, in these zones, cracks and therefore zones of weakness which are incompatible with the mechanical strength of the transverse member.
The object of the invention is to avoid these drawbacks by proposing a transverse member whose torsional stiffness can be altered according to the characteristics sought for the rear axle assembly and which makes it possible to reduce the cross section and/or the wall thickness, and therefore the weight of the motor vehicle.
The subject of the invention is therefore a deformable transverse member for a motor vehicle, especially a rear axle assembly with trailing arms, characterized in that it is formed of a metal section piece comprising a continuous longitudinal opening extending along at least 80% of the length of the further section piece and in that it is fitted with a block of elastomeric material fastened to the section piece and closing off the central part of the longitudinal opening.
According to other features of the invention:
the section piece has several faces and the face comprising the longitudinal opening has two opposed turned-down edges against which the block of elastomeric material rests,
the block is formed of a sheet which has a cross section in the shape of a quadrilateral,
the block is formed of a sheet which has a U-shaped cross section,
the block has vertical side edges or parallel and inclined side edges,
the block is fastened to the section piece by bonding or by screw fasteners, and
the elastomeric material of the block has a Young""s modulus of between 200 and 500 MPa.
The invention will be better understood from reading the description which will follow, given merely by way of example, for an understanding of which reference will be made to the appended drawings, in: